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2001 Hyundai Tiberon - Unsolvable Random misfire codes - help!!!

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Aug 14, 2015, 11:26 AM

Post #1 of 2 (1130 views)
2001 Hyundai Tiberon - Unsolvable Random misfire codes - help!!! Sign In

2001 Hyundai Tiberon A/T - Random Misfire codes and I believe we have tried nearly everything. Car throws P0300 all the time between 40-60 mph, Throws P0301, 0304 nearly as many times at the same speeds, and once in a while will throw p0302. The vehicle has 75K miles on it and runs well - no noticeable misfire problem, however, some have said it feels under-powered. Here is what's been done, looked at and verified its correct or working. (Not necessarily in this order). My question is what else could it be and how can we test it?

Crank trigger replaced (2 times - 1 of the replacements was bad)
Compression checked out within spec
No intake vacuum leaks - all vacuum specs within factory tolerance
Brand new coil
New spark plug wires
New Iridium spark plugs
Mass air flow sensor verified to be functioning within spec
Timing belt (double verified when replaced to be properly installed on cam and crank marks).
Both o2 sensors within spec and functioning - one was replaced because it was a bit off.

Basically, we have gone through the typical and Atypical issues that can cause these codes. Neither my nor my mechanics equipment is sensitive enough to detect why this code continues to be thrown?

Our last thought is it's the ECU "brain Box" and it's malfunctioning? We have not tried a different ECU.

Open to ideas?

Tom Greenleaf
Ultimate Carjunky / Moderator
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Aug 14, 2015, 11:57 AM

Post #2 of 2 (1122 views)
Re: 2001 Hyundai Tiberon - Unsolvable Random misfire codes - help!!! Sign In

Just two thoughts for now on this:

Was crank sensor bad or possible to be installed improperly? It's just bad parts if lots has been done hard to trust new from that source or maker?

Plugs: Some vehicles are very fussy about OE only plugs. IDK the exact ones right now but only use those. No magic - the ones it was originally designed for with no tricky claims of anything.

At the MPH you notice this is also where a torque converter will lock up depending on load on engine. That alone is a quick load on engine being a higher gear ratio still at some RPM and a spot spark is really needed to be accurate. Just know it's harder for a plug to make a good spark while under higher compression for times it is than plain idle - wrong plugs not usually that dramatic but should be right ones only when things aren't working properly don't add that to the list of possible reasons,


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